Lithium ion batteries are increasingly used as the electric power source in electric (EV) and plug-in hybrid electric (PHEV) vehicles. This is due to the higher energy per mass and higher energy per volume characteristics that lithium ion batteries offer versus existing battery technologies such as nickel-metal hydride, nickel-zinc and lead-acid battery systems. Rechargeable batteries are also referred to as secondary batteries, and lithium ion secondary batteries generally have a negative electrode material that intercalates lithium. For some current commercial batteries, the negative electrode material can be a carbonaceous or graphitic material, and the positive electrode material can comprise lithium cobalt oxide (LiCoO2). In practice, only a relatively modest fraction of the theoretical capacity of the cathode can be used. At least two other lithium-based cathode materials are also currently in commercial use. These two materials are LiMn2O4, having a spinel structure, and LiFePO4, having an olivine structure. These other materials have not provided any significant improvements in energy density.
Lithium ion batteries can be designed based on their application. One design category involves high energy batteries, whereby lithium ion battery cells are designed to deliver low to moderate current (Amperes) for such applications as cellular phones, lap-top computers, Electric Vehicles (EVs) and Plug in Hybrid Electric Vehicles (PHEVs) with the delivery of higher total capacity. The high energy batteries can be designed to operate with moderate rate performance. In contrast, if the battery is designed for higher rate performance, the total energy that can be delivered from the battery generally is reduced.